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Clinical and Laboratory Studies on Herds Affected with PMWS in Denmark, France, Spain and Sweden

31 May 2012

With the aim to establish a protocol to diagnose post–weaning multi–systemic wasting syndrome (PMWS) at herd level, a multinational group of researchers in Europe has concluded that likely indicators are a significant increase in post–weaning mortality in addition to clinical signs and PMWS must be diagnosed in at least one of three to five pigs while the mortality is elevated.

In the current issue of Journal of Swine Health and Production, a group of experts on postweaning multisystemic wasting syndrome (PMWS) from across Europe report their work into the progression of the disease and a proposal for herd case definition. The first author was Dr Llorenc Grau-Roma of Spain’s Universitat Autònoma de Barcelona and co-authors also represented the Danish Agriculture and Food Council, Agence Française de Sécurité Sanitaire des Aliments (AFSSA) in Ploufragan, France, Sweden's National Veterinary Institute, Institut de Recerca i Tecnologia Agroalimentàries (IRTA) in Spain and the Technical University of Denmark in Kalvehave.

Their primary objective was to propose and evaluate a protocol to establish a diagnosis of PMWS at herd level.

The data used included both laboratory data from previous epidemiological studies carried out in Italy, Denmark and Spain and original post–weaning mortality data collected from several herds in Denmark, France, Spain and Sweden. Statistical process control techniques were used to analyze the longitudinal evolution of mortality in each herd.

The analysis of data sets from three different countries showed that to diagnose at least one PMWS–affected pig with a probability more than 95 per cent, it is necessary to study a minimum of three to five pigs. Longitudinally collected data showed that when more than 20 data points were available, a significant increase in mortality was always detected at close to the time of PMWS diagnosis. When fewer than 10 points were available, a significant increase in mortality was detected in four of six studied herds, although mortality percentages were always higher at the time of PMWS diagnosis than before diagnosis.

These results suggest that two conditions must be fulfilled to diagnose PMWS in a herd, concluded Grau-Roma and co-authors. Firstly, a significant increase in post–weaning mortality – compared to the historical background in the herd – must be observed in association with clinical signs compatible with PMWS. Secondly, PMWS must be diagnosed in at least one of three to five necropsied pigs concurrently with the increase in mortality. They added that it is necessary also to rule out other potential causes of increased mortality.